Unit for recovery of plating solution



Nv- 24,.-'1970 AlsABUR-'o YAGlsHlTA Y "3,542,551

n UNIT FOR RECOVERY l0F PLATING SOLUTION mea oct. 1e. 196e IN VEN TOR.

' s sheets-sheet 2v NOV- 24, 1970 AlsAauRo wkeslssmwuV v 3,542,651 UNIT Fon RECOVERY F PLATING SOLUTION mea otl.j1e. 196e Y s sheets-sheet s IN VEN TOR. vuuro )"Jgvln't v BY United States Patent O U.S. Cl. 202-169 3 Claims ABSTRACT OF THE DISCLOSURE For reclaiming platting wastes containing chromic acid and the like, a plurality of wash tubs are provided into which plated articles are dipped successively to rinse off the plating solution. The tub Water from the tub, into which the articles are first dipped, is sucked into a tower heated by steam to concentrate the tub water to plating strength; and this water is returned to the plating tank. Water is siphoned from the other tubs successively back to the first tub. The vapor in the tower is used in a condenser to heat water owing to the tub most remote from said Ifirst tub, to replenish the system. The tower has an inner container; and the tower proper and the space between this container and the tower proper is held under vacuum.

This invention relates to a unit for disposal of plant wastes. More particularly, this invention relates to a unit for recovery of wastes from metal finishing plants, such as plating wastes containing chromic acid and the like.

In a number of industries involving the operation of rinsing the products from chemical treatment processes, the amount of effective chemicals in the rinse liquid is considerable, and recovery of such chemicals has had a great economical significance. Moreover, such rinse liquid as a caustic soda solution from a mercerizing process in the fiber industry or a. plating solution in the plating industry would result in considerable pollution of streams if they were discharged from rinsing operations following mercerizing or plating operations. Thus, the recovery of such chemicals has been regarded as a necessity from the standpoint of conservation of stream water quality.

In general, the kind of chemicals in the rinse liquids varies from one rinsing operation to another. Most of these liquids are appreciably diluted solutions as cornpared with the original plating solution, and recovery of the chemicals in the rinse liquid is a matter of difficulty because of the expense involved. In a minority of cases, recovery of the expensive chemicals is planned, however, the bulk of such chemicals are discharged from rinsing operations following chemical treatment processes; and a recovery unit that might work out in a most economical and simplified manner has been in demand.

Hence, an object of the present invention is to provide a unit which attains recovery of chemicals contained in a rinse liquid in an economical and simplified manner by rationalizing the usage of rinse liquid either through collecting highly contaminated liquid and returning the same to the opertaing tank, such as a plating tank, or transferring the liquid to the heating and concentrating tower for concentration, depending on the concentration or level of the liquid contained in the operating tank.

Another object of the present invention is to provide a recovery unit wherein Waste water containing toxic chemicals is not discharged from the plant and savings of effluent wat remay be attained.

A further object of the present invention is to provide a recovery unit equipped with a heating and concentrating tower which is of the double-walled construction comprising the heating and concentrating tower proper and 3,542,651 Patented Nov. 24, 1970 a noncorrosive inner container fixed and secured to such portion of the heating and concentrating tower proper which requires the greatest degree of noncorrosiveness, the space between the tower proper and the inner container being connected to the inside of the inner container so as to establish the same degree of vacuum in the inside of said space as in the inside of the inner container, thus increasing the noncorrosiveness and durability of the tower, while saving the expensive corrosion-resistant materials that go to make up the heating and concentrating tower, and attaining improvement in heat insulation property, with a view to reducing the fuel costs.

A further object of the present invention is to provide a plant Waste recovery unit equipped with a heating and concentrating tower which performs the dual function of disposal of Waste and recovery of effective chemicals mixed in the rinse liquid through raising the temperature of the operating tank containing the plating solution and the like and concentrating the dilute solutions contained in the rinse liquid by simply adjusting the valves and thereby making or breaking the circuits.

A further object of the present invention is to provide a recovery unit so made that cooling water passingthrough an ejector is entrained in the vapor stream from the heating and concentrating tower iitted to the plant waste recovery unit and the vapor is condensed through cooling in the cooling water, and wherein means is provided to prevent backflow of such cooling water into said heating and concentrating tower via the route of exhaust vapor and resulting dilution of the concentration of the liquid contained in the tower.

A still further object of the present invention is to provide a plant waste disposal unit so made that the rinse water containing a minor quantity of plating solution etc. adhering to the ware being transferred to the wash water tubs is passed through an ion exchange resin layer for adsorption and removal of ions and the purified water lthus obtained through ion exchange is circulated to the wash water tub for reuse as wash water, while the hot water from the condenser connected to the heating and concentrating tower is admitted into the hot wash water tub in the series of the wash water tube to be used as hot wash Water.

A still further object of the present invention is to provide a plant waste disposal unit equipped with ion exchange tower which entails hardly any expenses in the regeneration of the ion exchange resins.

Now, the present invention will be described hereinbelow with reference to certain embodiments thereof as illustrated in the accompanying drawings, in which:

FIG. l is an explanatory view showing a recovery unit equipped with a heating and concentrating tower according to the present invention;

FIG. 2 is a partially cut side elevational view showing an embodiment of the heating and concentrating tower fitted to the recovery unit as shown in FIG. l;

FIG. 3 is a view similar to FIG. 2 but showing, in side elevation, another embodiment of the heating and concentrating tower fitted to the recovery unit;

FIG. 4 is a sectional view showing an embodiment of the condenser unit fitted to the recovery unit as shown in FIG. l;

FIG. 5 is a wiring diagram illustrating the electrical connections in the trap device installed in the recovery unit of FIG. l;

FIG. 6 is an explanatory view showing the recovery unit of FIG. l equipped with ion exchanger; and

FIG. 7 is a partially cut side elevational view showing another embodiment of ion exchanger means as shown in FIG. 6.

In each drawing, the corresponding parts are designated by the corresponding numerals.

Referring to FIG. 1, by way of giving a detailed explanation of the unit according to the present invention, a plurality of wash water tubs 2, 3, 4, are connected in series with the plating tank 1, the fourth tub 2 among the wash water tubs serving as the hot wash water tub.

The wash water tubs 2, 3, 4, 5 are connected one with the other by means of siphons 15, 16 and 17, and the fourth tub 2 is tted with an overow pipe 14. To the rst wash water tub 5 is connected a heating and concentrating tower 7 via a feed pipe 6. Heating of the liquid to be concentrated is effected by means of the steam sent forth into the heating unit 12 enclosed inside said tower via pipe 18 and waste steam is exhausted via pipe 19. Furthermore, a condenser unit is annexed to the heating and concentrating tower 7 to condense the vapor evaporated from the tub water supplied into said tower and heated by the heating steam'. Cooling water is passed through helically wound cooling pipe 11 inserted into said unit 10 and the hot water heat exchanged in the condenser unit 10 is passed through said cooling pipe 11 and is supplied to the fourth wash water tube or hot wash water tub 2. Tub water in the first Wash water tub 5 pumped into the heating and concentrating tower 7 via feed pipe 6 is heated and concentrated to the level equivalent to that of the plating solution contained in the plating tank 1 before it is restored to the plating tank via pipe 8. Water is supplied at times to the warm wash water tub 2 via pipe 13.

Supposing that plating operation comprising moving the plated ware from the plating tank and immersing the same consecutively in a series of wash Water tubs is conducted in a chromium plating plant employing 10 kg. of chromic acid per eight hours a day, and that the capacity of the rst wash water tub 5 is 200 l., the metallic articles plated in the plating tank 1 are washed consecutively in the wash water tubs 5, 4, 3 and finally in the hot water tub 2. If the recovery unit according to the present invention is not utilized, approximately 85 percent of chromic acid contained in the plating tank 1 goes onto the plated ware and is carried oil the plating tank 1, and the chromic acid concentration levels of the Wash water tubs 5, 4, 3 when the operation is iinished are approximately 45 g./1., 6.5 g./l. and 0.6 g./l., respectively.

On the other hand, if the recovery unit according to the present invention is utilized, supposing that the evaporative capacity of the heating and concentrating tower 7 is 100 kg./h. and that the capacity of the rst wash water tub 5 is 200` 1. and other conditions are also same as above, the tub water contained in the tub 5 is diminished by one-half per hour, and the tub 5 is supplied with wash water from the second, third and fourth wash water tubs by means of siphones 15, 16, 17. The wash water contained in the wash water tubs 5, 4, 3 is diluted and chromic acid concentration levels of the tubs 5, 4, 3` are maintained respectively at 15 g./1., 1 g./l. and 0.08 g./1., or thereabout.

As will be seen from the above, the concentration levels of the second and third wash water tubs 4, 3 are so low that, needless to say, concentration of wash water contained in these tubs cannot be attained on an economical basis.

Hence, an ion exchange column 21 as shown in FIG. 6 may be annexed for instance to the second water tub 4. In this embodiment, tub water contained in the wash water tub 4 is pumped via pipe 20 and is passed through the exchange column 21 compulsorily where tub water is placed in contact with anion exchange resin layer 22 provided said column and chromic acid etc. are adsorbed to the resin layer 22 and removed. The purified water from the column 21 may be returned to the wash tub 4 for reuse as wash water.

The gauges of the pipes and 23 are so designed that prescribed flow rate of wash water circulating through pipes 20, 23 may be established to elect prompt removal of chromic acid etc. carried into the wash water tub 4 along with the plated articles. Normally, such capacity may be ten times the capacity of the wash water tub 4.

In treating tub water containing chromic acid, the reaction of cation exchange resin contained in the cation exchange resin column 21 is shown as follows:

In regenerating the cation exchange resin saturated with chromic acid, the tank 25 is filled with vregenerant such as 4% caustic soda solution and the said tank 25 is supplied with barium hydroxide in a suitable amount from the feeder 55. In the first place, caustic soda solution is pumped into the ion exchange column 21 via a pipe 26 opened at one end into said tank 25 and at the other end into the lid of the ion exchange column 22 for regeneration of the cation exchange resin layer whereby a reaction takes place as shown in the following scheme.

The chromic acid adsorbed to the cation exchange resin layer is discharged into the regenerant tank 2S via a drain pipe 24 as sodium chromate solution together with excess caustic soda solution, where the sodium chromate solution is reacted with barium hydroxide which is almost insoluble in the caustic soda solution and is converted t0 barium chromate, as shown in the following.

The barium chromate is then filtered off by a filter 27 and caustic soda solution alone is supplied to the exchange column 21 to repeat the abovementioned reaction.

Referring to the unit shown in FIG. 6, the tub water contained in the first wash water tub 5 with utmost chromic acid concentration is supplied to the heating and concentrating tower 7 for heating and concentration and recovered to the plating tube 1, while the tub water in the wash tub 4 situated ahead of the hot wash Water tub 2 containing a minor quantity of plating solution carried olii` the Wash Water tub 5 together with the plated articles is pumped into the cation exchange column 21 to remove plating chemicals through ion exchange. Purified water from cation exchange column 21 is restored to the wash water tub 4 for use as wash Water. On the other hand, cooling water is passed through helical pipe 11 in the condenser unit 10 of the heating and concentrating tower 7 for cooling of the vapor, and, heated, is supplied to the hot wash water tub 2 for use as hot wash water which rinses the plated metal articles and consequently dries them.

Heating and concentration of tub water in the heating and concentrating tower 7 in the present recovery unit may be conducted most effectively under vacuum. Moreover, since tub water contains metal corrosive chemicals, such as chromic acid and so forth, the tower must be both noncorrosive and pressure-resisting. An embodiment of the tower which fulfills above requirements is shown in FIG. 2. The tower 7 illustrated in the figure has a doublewalled construction comprising the tower proper and an inner container wherein the inner container is especially constructed from noncorrosive materials to attain reduction in the production costs and wherein the degree of vacuum in the inside of the space between the tower proper and the inner container is maintained the same as in the inside of the inner container to prevent generation of strain or destruction of the latter, due to negative pressure, and to enhance its durability and heat insulation property.

As illustrated in FIG. 2, heating and concentrating tower 7 is made up of two parts connected together, i.e., lower cylindrical member 29 and upper cylindrical member 28. A flange 32 is formed on the inside periphery of the upper cylindrical member 28. The inner container 30 is made from noncorrosive material and is situated in the inside of the lower cylindrical member 29 so as to cover the inner surface thereof. The liange 31 on the upper outside periphery thereof is tightly tted and secured to the ange 32 to provide the double-walled construction with a space between the inner container 30 and the inside of the lower cylindrical member 29. The inner container 30 is a heater and has a heating device 12 towards the lower part thereof to heat the liquid contained in the container 32 through steam or other heat source. Evaporated vapor is sent upwardly to completely fill the upper portion of the upper cylindrical member 28. On top of the upper cylindrical member 28, a device 33 for prevention of spray is provided and is connected to the condenser unit via connecting pipe 9. Pressure adaptor pipe 34 branched from connecting pipe 9 is connected to the space formed between the inner container 30 and the inside of the lower cylindrical member 29. A vacuum pump is litted to the condenser unit 10 via cooling water supply pipe 11 and, in a known manner, the degree of vacuum in the heating and concentrating tower is maintained at a predetermined value by the suction exerted by a vacuum pump.

The saving or reduction of corrosion-resistant material may be attained since the inner container 30 need only be imparted such rigidity as to withstand the weight of the liquid stored therein for concentration.

In consequence of this, the heating and concentrating tower need not be constructed from single noncorrosive material as a whole and, moreover, since the space between the inner container and the tower proper is connected to the inside of the evacuated heating and concentrating tower so as to keep the pressures in the inside and outside of the inner container practically equal, the inner container of the most brittle construction does not become impaired under negative pressure due to vacuum. Moreover, since convection of heat via said space is prevented due to vacuum established in said portion, dissipation of heat from the evaporator may be prevented effectively, resulting in an improvement in the maintenance of temperature.

FIG. 3 shows another embodiment of the heating and concentrating tower of the present recovery unit wherein elevation and maintenance of temperature of the plating Solution and concentration of the n'nse water of the wash water tub containing plating solution may be eifected at the same time.

In the rst instance, in starting the plating operation such as copper plating operation, the plating solution must be elevated in tempertaure. So, the plating solution in the plating tank 1 ispumped into the heating and concentrating tower 7 via a suction pipe 38, valve, and exhaust pipe 18 and, after being heated in the heating pipe 35 installed in the tower, is returned to the plating tank 1 via a pipe 8 when a predetermined temperature is attained. All heating pipes 35 installed in the tower 7 are in this instance utilized to raise the temperature of the plating solution, so the elevation of temperature may be attained in a short period of time. Admission and exhaust of heating steam is by way of the inlet and outlet ports 18 and 19.

4 With elevation of temperature of the plating solution, or when the latter has attained a predetermined temperature, the plating operation is started. As the articles plated in the tub -1 are transferred to the wash water tub 5, dragout of a large quantity of plating solution containing effective chemicals takes place. So, the tub water in the wash tub 5 is gradually contaminated, resulting in an increased concentration. When the tub water has reached or exceeded a certain level of concentration, a pump installed in a suction pipe 6 opening at its one end in the wash water tub is set in operation, and tub water is admitted into the heating and concentrating tower 7 via said suction pipe 6, valve and exhaust pipe 18. Tub water heated by the heating pipes 35 is boiled and sent upwardly and then downwardly by way of the downtake 12 for reheating. This process is repeated in the manner as above described and the rinse Water concentrated to the level of concentration of the plating solution 1 is re- 6 turned to the plating tub 1 via an outlet pipe 8. As the plating operation proceeds, relatively cool articles are dipped in the plating tub 1 successively, and the plating solution is cooled down gradually in addition to the fact that the cooling of the plating solutionis promoted by the dissipation of heat from tub Wall and liquid surface. In order to keep the plating solution at a constant temperature, plating solution is pumped at all times into the heating pipe 39 enclosing downtake 12 via suction pipe 38 by means of a pump and, after being heated there, is returned to the plating tub 1.

In case that the rinse liquid is concentrated and does not require concentration, part or all of the rinse liquid is heated in the heating pipe 39 via suction pipe 6 and pipe 37 and returned direct to the plating tub 1.

lFIGS. 4 and 5 show embodiments of the condenser installed in the present recovery unit.

Heating device 12 is accommodated inside the heating and concentrating tower 7 and the liquid stored in the tower for concentration is heated and evaporated by the steam supplied from piping 18. The evaporated vapor passes through. the device for prevention of spray 33 and pipe 9 and, swinging the swing valve 41 of the check valve 40 open, reaches an ejector 42. Cooling water from the reservoir 43 is pumped into the ejector 42 via pipe 45 by means of a pump 44. Cooling water is pumped from the cooling water tub 43 into the ejector 42 via pipe 45 by a pump 44 and is entrained in the vapor stream from the heating and concentrating tower 7 and vapor cooled and condensed in the cooling water is exhausted to the hotwell 46 and discharged. Vacuum is maintained in the heating and concentrating tower 7 due to suction of vapor effected by the ejector 42 to lower the boiling point of the liquid to be concentrated and promote its evaporation.

In actual operation of the abovementioned device, the degree of vacuum in the heating and concentrating tower 7 is not always constant and, moreover, the supply of heating steam to the heating device 12 varies from time to time. So, the liquid to be concentrated is boiled and vaporized intermittently and the exhaust vapor from pipe 9 causes vibration of the swing valve 41. In addition, cooling water pumped by the pump 44 into the ejector 42 collides with vapor supplied intermittently, with the result that the temperature of the cooling water is elevated and lowered cyclically and the performance of the ejector 42 is fluctuated. This causes further vibration of the swing valve 41 until the check valve 40 is rendered inoperative and the cooling Water is reversed to the concentrating tower 7 under reduced pressure to dilute the liquid therein.

It is apparent that the possibility of reversal of cooling water will be increased in the case of vacuum heating and concentrating device without the provision of check valve 40.

4In order to overcome such deficiency, a trap 48 consisting of a hermetically sealed vessel is connected to the perpendicular branch pipe 47 iitted to the mid portion of the pipe 9 connecting the concentrating tower 7 and the ejector 42 in a closed loop. In this way, cooling water reversed from the ejector 42 via pipe 9 may be stored inside the trap 48 and prevented from entering the concentrating tower 7.

A liquid level detector 50 is placed in the trap 48 so as to control the operation of the liquid level controller 51.

Such liquid level detector 50 may consist of a pair of electrodes which may be connected electrically as the cooling water stored in the trap 48 reaches a certain level and the ends thereof are immersed in the water. In the arrangement above described, as the cooling water in the trap 48 reaches a certain level, the pump 44 is stopped automatically and does not come into operation until the drain cock 49 of the trap 48 is opened to eX- haust collected cooling water.

FIG. 5 shows an example of a simple electrical wiring 7 of this kind of trap device. In this example, liquid level controller 51 is a relay and its coil is inserted in the control circuit '52 in which is inserted a liquid level detector 50, while a normally closed tap is inserted in the circuit 53 for driving the pump 44.

FIG. 7 shows another embodiment of the ion exchange resin regenerating device as mentioned previously with reference to F-IG. 6 wherein a water permeable vessel is accommodated in the regenerant tub Z5. This vessel contains barium hydroxide which is almost insoluble in caustic soda solution and is stirred up by a stirrer 56. Other members are the same as those mentioned with reference to FIG. 6.

For better results, the pipes 8 and 6 of the recovery unit of the present invention as shown in FIGS. 1 or 6 may be provided respectively with chemically reacting rfilter and a cation exchange coulmn to remove impurities contained in the tub water.

What is claimed is:

1. A unit for recovery of wastes from metal linishing plants, such as plating Wastes containing chromic acid and the like, comprising a plating tank, a plurality of Wash water tubs in serial communication by siphon means, including a hot wash water tub, into which the plated metal articles transferred from said plating tank are to be dipped consecutively to rinse out the plating solution adhering to said articles, means to suck up tub water contained in the rst wash water tub into which the plated metal articles are dipped first, a heating and concentrating tower to receive the tub water sucked up by the aforementioned means and to concentrate said tub water to the plating strength, a pipe opening at one end into said heating and concentrating tower and at its other end into said plating tank to convey the tub water, which is concentrated to plating strength in the heating and concentrating tower, to the plating tank, a condenser connected to said heating and concentrating tower and including a pipe which passes through said condenser and communicates with said hot wash water tub for supplying fresh water to said hot wash water tub, the vapor from the tub water heated in the heating and concentrating tower being condensed in consequence of heating said fresh water, and means for conveying the condensation from said condenser to said hot water wash tub.

2. A unit for recovery of wastes from metal finishing plants, such as plating wastes containing chromic acid and the like as claimed in claim 1, wherein said heating and concentrating tower includes a pair of cylindrical members, each of said members having an open end hermetically juxtaposed against an open end of the other member, and an inner container of relatively thin-walled non-corrosive material having suicient capacity to accommodate tub water supplied into the tower from said lirst wash water tub, and having its outer peripheral surface adjacent one end thereof sealingly and removably engaged with the inner wall of one of said members and extenling into the other of said members in radially spaced relation to the inner wall thereof.

3. A unit for recovery of wastes from metal nishing plants, such as plating wastes containing chromic acid and the like as claimed in claim 2, including a vacuum pump connected to said tower to maintain the inside thereof under vacuum, and means connecting the inside of said tower with the radial space formed between said inner container and said inner wall of said other member to maintain the pressure inside said tower substantially equal to the pressure in said radial space so that the container does not undergo deformation in spite of the thinness of its wall.

References Cited UNITED STATES PATENTS 2,626,621 1/1953 Curtis 204-203 XR 2,853,442 9/1958 Swanton 204-28 2,984,081 5/1961 Hahn 204-239 XR OTHER REFERENCES `Graham et al., Electroplating 'Engineering Handbook, 2nd ed., 1962, Reinhold Pub. Corp., New York, pp. 344- 348.

Morisset et al., Chromium Plating, 1954, lRobert Draper, LTD. Teddington, England, pp. 529-533.

Swanton, Plating, vol. 46, pp. 919-921 (1959).

NORMAN YUDKOFF, Primary Examiner R. T. FOSTER, Assistant Examiner U.S. Cl. XR. 

